The invention relates to a method of obtaining a pattern of concave spaces or apertures in a plate or layer of a brittle-like material, in which method a jet of abrasive powder particles from a nozzle is directed onto a surface of the plate or layer, which plate or layer is provided with a mask so as to define the region of impact of the abrasive powder particles on the surface. The invention also relates to a brittle-like material provided with such a pattern of concave spaces or apertures, and to the special application of such a brittle-like material.
The method mentioned in the opening paragraph is known per se from the previously filed European patent application 0 660 360 in the name of the Applicant. In accordance with the method of powder blasting, particles collide at a high velocity with a substrate, particularly glass. After the impact, they generate local damage in the substrate which may lead to the removal of the small fragments from the surface. This process is iterated many times and may thus be considered as an erosion process. A glass plate having a thickness of 0.7 mm is thus provided with a metal mask. The metal mask is adhered to the plate by means of an adhesive layer so as to prevent local delamination during the powder blasting process. A spraying unit provided with a nozzle is directed onto the surface of the plate, while a jet of abrasive powder particles, for example, silicon carbide or aluminum oxide leaves the nozzle on the basis of the pressure or venturi principle and lands on the surface of the plate or layer so as to form concave spaces or apertures therein. The angle at which the jet of abrasive powder particles extends to the plate or layer is thus 90xc2x0. It is further known from this European patent application to use a plurality of nozzles, while the plate performs, for example, an iterative movement parallel to the X axis and the spraying unit performs a movement parallel to the Y axis, with both velocities being adapted to each other in such a way that the desired aperture or pattern of concave spaces, particularly ducts, is obtained in the plate. For obtaining a better homogeneity of the desired pattern, it is also known from this document to use a plurality of nozzles, each of which is passed across a part of the mask. A drawback of such a method is that the jet of abrasive powder particles directed perpendicularly to the surface of the plate makes a hole of a special shape in the plate or layer. The manufacture of substantially symmetrical concave spaces or apertures having flat bottoms is, however, not possible with such a method. Moreover, the reproducible construction of concave spaces or apertures having substantially straight side walls is not possible.
It is therefore an object of the present invention to provide a method of obtaining a pattern of concave spaces or apertures in a plate or layer of a brittle-like material, which concave spaces or apertures are characterized by a substantially flat bottom.
Another object of the present invention is to provide a method of obtaining a pattern of concave spaces or apertures in a plate or layer of a brittle-like material, which spaces or apertures have substantially straight side walls.
Another object of the invention is to provide a method of obtaining a pattern of concave spaces or apertures in a plate or layer of a brittle-like material, which spaces or apertures are interconnected.
According to the invention, the method described in the opening paragraph is characterized in that at least two jets of abrasive powder particles are each directed at respective angles of xcex11 and xcex12 onto the surface of the plate or layer, which jets mutually extend at an angle of (180xc2x0-xcex11-2), the shape of the concave spaces or apertures thus formed being not limited by the thickness of the brittle-like material.
The part of the phrase xe2x80x9cat least two jets of abrasive powder particlesxe2x80x9d in the introduction and the claims should be considered as an embodiment in which the surface of the plate or layer is always powder-blasted at an angle. It is thus possible to place a nozzle at an angle xcex11 and to subsequently place the same nozzle at an angle xcex12, which embodiment falls within the protective scope of the present invention. It is also possible to vary the angle xcex11 at which the nozzle extends to the surface of the plate or layer continuously or not continuously, which embodiment also falls within the protective scope of the present invention. In practice, two or more separate nozzles, each with a respective angle xcex11 and xcex12 will be used from a production-technical point of view.
The term xe2x80x9cbrittle-like materialxe2x80x9d mentioned in the introduction and the claims should be considered as a material in which concave spaces or apertures can be provided by means of powder blasting, for which notably glass, ceramic material, silicon and brittle synthetic materials are suitable basic materials.
The part of the phrase xe2x80x9cnot limited by the thickness of the brittle-like materialxe2x80x9d mentioned in the introduction and claims should be understood to mean that the method is suitable for providing apertures or concave spaces in any brittle-like material or combinations of one or more brittle-like materials in which the apertures or concave spaces formed extend partly or completely across the thickness of the material or combination of materials used. The shape of the apertures or concave spaces thus formed is not defined by a possible transition of material properties, as is the case in the Japanese patent publication 082 22129 to be described hereinafter. Consequently, a hard, brittle-like material as a stopper layer is not required.
Although it is known from the Japanese patent application published under no. 082 22129 on Aug. 30, 1996 to make a concave space in a brittle-like material while using a jet of abrasive powder particles, it is necessary for the method known from this publication that the brittle-like material essentially consists of two separate materials, namely a relatively soft brittle-like material and a hard brittle-like material. The relatively soft brittle-like material is provided with a mask which is subsequently subjected to the powder-blasting treatment so that the soft brittle-like material not shielded by the mask is removed by the powder particles. The concave spaces are thus only formed in the soft brittle-like material, while the transition from the relatively soft brittle-like material to the hard brittle-like material serves as a stopper layer. A concave space thus formed has a flat bottom which is formed by the hard brittle-like material that has not been removed by the jet of abrasive powder particles. Moreover, this Japanese patent application does not give any information about the special angle of the jet of abrasive powder particles with respect to the surface of the plate or layer in which the pattern of concave spaces or apertures is formed. Frit is used as a relatively soft brittle-like material, and glass is used as a hard brittle-like material. A drawback of this technology is that a top layer of frit should always be provided on the hard brittle-like material, which treatment has a cost-increasing effect. Moreover, the released frit must be removed.
The angles xcex11 and angle xcex12 used in the method according to the invention are preferably between 30xc2x0 and 80xc2x0, particularly between 45xc2x0 and 65xc2x0.
The use of such angles xcex11 and xcex12 has led to concave spaces or apertures with a substantially flat bottom. If the angles xcex11, angle xcex12 are smaller than 30xc2x0, the erosion speed is low, which is undesirable for practical applications. If, in contrast, the angles xcex11, angle xcex12 are larger than 80xc2x0, the ducts formed on the lower side as compared with ducts obtained by means of powder blasting at an angle of 90xc2x0 will hardly widen, which is detrimental for obtaining symmetrical concave spaces or apertures having a substantially flat bottom and substantially straight side walls. It should, however, be clear that the present invention is not limited to apertures or holes with a flat bottom and/or straight side walls. In accordance with the method, it is alternatively possible to form apertures which are interconnected under the surface. Moreover, in accordance with the present invention, apertures or concave spaces can be obtained which extend throughout the thickness of the brittle-like material.
If ducts or grooves or slits must be formed in a plate or layer of the brittle-like material, it is preferred in the present invention to perform a relative movement between the jet of abrasive powder particles and the plate or layer. For an accurate and reproducible powder supply through the nozzle, it is preferred that the nozzle is situated at a fixed point.
To prevent interference of the jets of abrasive powder particles, causing a loss of kinetic energy, it is preferred to obtain a pattern of concave spaces or apertures in steps, in which the two jets of abrasive powder particles are directed one after the other onto the surface of the plate or layer. This consecutive operation should also include the embodiment in which the formation of the apertures or concave spaces takes place with a fast alternation of both jets. In accordance with such a high-frequency alternation of both powder jets, it is possible to obtain a symmetrical concave space or aperture.
In a particular embodiment of the present invention, it is further preferred to direct the two jets of abrasive powder particles onto separate positions of the plate or layer so that the powder blasting efficiency is influenced in a favorable manner.
Experiments have proved that it is desirable that the geometry or dimension of the nozzle for both jets of powder particles is substantially identical for obtaining substantially symmetrical concave spaces or apertures in a plate or layer of the brittle-like material. Moreover, for obtaining such symmetrical concave spaces or apertures provided with a flat bottom, it is preferred that the kinetic energy determined by the size and velocity of the powder particles is substantially identical for both jets of powder particles, while it is notably preferred that angle xcex11 is equal to angle xcex12. Moreover, in such an embodiment it is preferred that the quantity of particles, namely the powder flux, is substantially identical for both jets of powder particles.
To be able to check the kinetic energy of the particles, it is necessary that both the size of the particles and their velocity should be determined accurately. In given embodiments, it is thus preferred that the abrasive powder particles have a size of between 10 and 50 xcexcm.
For obtaining a pattern of concave spaces or apertures in a plate or layer of the brittle-like material having a depth of 85 to 200 xcexcm, it is preferred that the mask has a thickness of between 30 and 100 xcexcm.
The present invention also relates to a brittle-like material provided with a pattern of concave spaces to apertures, which brittle-like material is characterized by the method as described in the present invention.
The brittle-like material obtained by means of the method according to the invention is notably suitable for use in plasma display panels (PDP), plasma-addressed liquid crystal displays (PALC) and in components for micro electromechanical systems, for example, sensors, actuators and micrometering systems.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.